1.功能
1.实现 管道（ | )
2.实现 输入输出重定向(<> >>)
3.实现 后台运行（ &）
4.实现 内建命令（cd ）
5.屏蔽一些信号（如ctrl + c 不能终止）
6.通过设置环境变量 可以直接使用 (在任意地方都可以运行你的shell)
2.代码分析
#include <stdio.h>
#include <stdlib.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <sys/wait.h>
#include <fcntl.h>
#include <unistd.h>
#include <string.h>
#include <pwd.h>
#include <dirent.h>
#define nomal 0 //默认情况
#define out 1 //输出重定向>
#define in 2 //输入重定向<
#define pipee 3 //管道|
#define outout 4 //输出重定向>>
void prompt(); //打印命令提示符
void get_param(char* param); //得到参数
int find(char* param); //查找命令
void cd(char *path); //内建cd
void anal(char* param, int* num, char arr[100][256]); //分析参数
void exec(int param_num, char para[100][256]); //执行命令
int main(int argc, char* argv[])
{
signal(SIGINT, SIG_IGN); //屏蔽ctrl+c
while(1)
{
int param_num = 0;
char *param = (char*) malloc (256);
char param_arr[100][256];
prompt();
get_param(param);
if((strcmp("exit", param) == 0 ) || (strcmp("logout", param) == 0))
break;
anal(param, ¶m_num, param_arr);
if(strcmp(param_arr[0],"cd") == 0)
{
cd(param_arr[1]);
continue;
}
exec(param_num, param_arr);
free(param);
}
return 0;
}
void prompt()
{
char hostname[500];
char buf[500];
struct passwd* id;
uid_t uid;
uid = geteuid();
id = getpwuid(uid); //得到用户名
gethostname(hostname, 500); //得到主机名
getcwd(buf, 500); //得到当前目录
printf("\033[32m%s@%s\033[0m:\033[34m%s\033[0m$ ", id->pw_name, hostname, buf);
}
void get_param(char* param)
{
char ch;
int i = 0;
do{
ch = getchar();
if(ch == '\n') break;
param[i++] = ch;
}while (1);
param[i] = '\0';
}
void anal(char* param, int* num, char arr[100][256])
{
char* p = param;
char* q = param;
int number = 0;
while(1)
{
if(p[0]=='\0')
break;
if(p[0]==' ')
p++;
else
{
q=p;
number=0;
while(q[0]!='\0' && q[0]!=' '){
q++;
number++;
}
strncpy(arr[*num],p,number+1);
arr[*num][number]='\0';
*num = *num+1;
p=q;
}
}
}
void exec(int param_num, char para[100][256])
{
pid_t pid;
pid_t pid2;
int fd;
int stat_val;
int stat_val2;
int i, x = 0;
int flag = 0;
int how = 0;
int bg = 0;
char* file;
char* arg[param_num+1];
char* arg1[param_num+1];
for(i = 0; i < param_num; i++)
{
arg[i] = (char*)para[i];
}
arg[param_num]=NULL;
if(!find(arg[0])) return;
for(i = 0; i < param_num; i++) //检测<,>,>>,|,&
{
if(strcmp(arg[i], "<") == 0)
{
flag++;
how = in;
}
if(strcmp(arg[i], ">" )== 0)
{
flag++;
how = out;
}
if(strcmp(arg[i], "|") == 0)
{
flag++;
how = pipee;
}
if(strcmp(arg[i], "&") == 0)
{
bg = 1;
}
if(strcmp(arg[i], ">>") == 0)
{
flag++;
how = outout;
}
}
if(flag > 1)
{
printf("param_num limit\n");
exit(1);
}
if(how == out)
{
for(i = 0; i < param_num; i++)
{
if(strcmp(para[i], ">") == 0)
{
arg[i] = NULL;
file = arg[i+1];
break;
}
}
}
if(how == in)
{
for(i = 0; i < param_num; i++)
{
if(strcmp(para[i], "<") == 0)
{
arg[i] = NULL;
file = arg[i+1];
break;
}
}
}
if(how == pipee)
{
for(i = 0; i < param_num; i++)
{
if(strcmp(para[i], "|") == 0)
{
arg[i] = NULL;
for(int j = i+1; j < param_num; j++, x++)
{
arg1[x] = para[j];
}
arg1[x+1] = NULL;
break;
}
}
}
if(how == outout)
{
for(i = 0; i < param_num; i++)
{
if(strcmp(para[i], ">>") == 0)
{
arg[i] = NULL;
file = arg[i+1];
break;
}
}
}
if((pid = vfork()) == -1)
{
printf("process creation failed\n");
exit(1);
}
switch (how){
case 0:
if(pid == 0)
{
execvp(arg[0], arg);
exit(0);
}
break;
case 1:
if(pid == 0)
{
fd = open(file, O_RDWR | O_CREAT | O_TRUNC, 0777);
dup2(fd, 1);
execvp(arg[0], arg);
exit(0);
}
break;
case 2:
if(pid == 0)
{
fd = open(file, O_RDONLY);
dup2(fd, 0);
execvp(arg[0], arg);
exit(0);
}
break;
case 3:
if(pid == 0)
{
pid2 = vfork();
if(pid2 == 0)
{
fd = open("./trans", O_RDWR | O_CREAT | O_TRUNC, 0777);
dup2(fd, 1);
execvp(arg[0], arg);
exit(0);
}
else
{
waitpid(pid2, &stat_val, 0);
fd = open("./trans", O_RDONLY);
dup2(fd, 0);
execvp(arg1[0], arg1);
exit(0);
}
}
break;
case 4:
if(pid == 0)
{
fd = open(file, O_RDWR | O_CREAT | O_APPEND, 0777);
dup2(fd, 1);
execvp(arg[0], arg);
exit(0);
}
break;
default:
break;
}
if(bg) return;
waitpid(pid, &stat_val, 0);
}
int find(char* param)
{
DIR* dir;
struct dirent* ptr;
int ice = 0;
dir = opendir("/bin");
readdir(dir);
while(ptr = readdir(dir))
{
if(strcmp(param, ptr->d_name) == 0)
return 1;
}
closedir(dir);
printf("Command '%s' not found\n", param);
return 0;
}
void cd(char *path)
{
if(chdir(path) < 0)
perror("chdir");
}